1. Technical Field
The present disclosure generally relates to well bore tools and in particular to methods and apparatus for estimating in-situ formation properties downhole.
2. Background Information
Oil and gas wells have been drilled at depths ranging from a few thousand feet to as deep as five miles. A large portion of the current drilling activity involves directional drilling that includes drilling boreholes deviated from vertical by a few degrees to horizontal boreholes, to increase the hydrocarbon production from earth formations.
Information about the subterranean formations traversed by the borehole may be obtained by any number of techniques. Techniques used to obtain formation information include obtaining one or more core samples of the subterranean formations and obtaining fluid samples produced from the subterranean formations these samplings are collectively referred to herein as formation sampling. Core samples are often retrieved from the borehole and tested in a rig-site or remote laboratory to determine properties of the core sample, which properties are used to estimate formation properties. Modern fluid sampling includes various downhole tests and sometimes fluid samples are retrieved for surface laboratory testing.
Laboratory tests suffer in that in-situ conditions must be recreated using laboratory test fixtures in order to obtain meaningful test results. These recreated conditions may not accurately reflect actual in-situ conditions and the core and fluid samples may have undergone irreversible changes in transit from the downhole location to the surface laboratory. Furthermore, downhole fluid tests do not provide information relating to formation direction and other rock properties.